Field of the Invention
The present invention relates to a method of aberration correction and a charged particle beam system.
Description of Related Art
In transmission electron microscopy, aberration correction is a technique that is important in obtaining high-resolution images.
For example, H. Rose, Optik, Vol. 85 (1990), pp. 19-24 and H. Haider et al., Nature, Vol. 392 (1998), pp. 768-769 disclose two-stage, three-fold field type spherical aberration correctors each having two stages of hexapole elements arranged therein. In these known spherical aberration correctors, positive spherical aberration in an objective lens is corrected by negative spherical aberration produced by the hexapole elements. Three-fold astigmatism produced in each hexapole element can also be canceled out by arranging the two stages of hexapole elements. In these two known spherical aberration correctors, up to the fourth order aberration can be corrected by axial alignment and other means. However, fifth-order, six-fold astigmatism cannot be corrected but rather remains as a dominant aberration.
H. Sawada et al., Journal of Electron Microscopy, Vol. 58 (2009), pp. 341-347 and H. Sawada et al., Ultramicroscopy 110 (2010), 958-961 disclose three-stage, three-fold field type spherical aberration correctors each having 3 stages of three-fold fields. Although the above-described two-stage, three-fold field type spherical aberration correctors cannot correct six-fold astigmatism, the spherical aberration correctors of H. Sawada et al., Journal of Electron Microscopy, Vol. 58 (2009), pp. 341-347 and H. Sawada et al., Ultramicroscopy 110 (2010), 958-961 correct six-fold astigmatism by means of three stages of three-fold fields.
JP-A-2012-109076 discloses a method of correcting five-fold astigmatism and three-lobe aberration in a three-stage, three-fold field type spherical aberration corrector. JP-A-2012-109076 also discloses a method of correcting on-axis aberrations.
As described previously, JP-A-2012-109076 discloses a method of correcting on-axis aberrations. However, there is not disclosed any method of correcting off-axis first order aberrations (defocus and two-fold astigmatism). Therefore, even if on-axis aberrations have been corrected in the center of the field of view, shifts of defocus and two-fold astigmatism may occur in off-center regions of the field of view.